The present invention relates to an illuminating apparatus for use in a liquid crystal display for television, a liquid crystal display for a computer and the like, which illuminating apparatus is provided in the back of a liquid crystal display device that displays a picture by modulating an optical state of light; and, in particular, the invention relates to an illumination apparatus having an improved and efficient collimating property and a liquid crystal display device using the same.
Recent technical developments and advancements the liquid crystal displays, and in particular, color liquid crystal displays, have been very remarkable, so that many types of color liquid crystal displays that feature a high performance display quality comparable to that of a cathode ray tube display are now on the market. Further, with the proliferation of note-type personal computers, any type of such liquid crystal display without provision of a back light illumination is not qualified for use as a commercial product, namely, the back light illumination is now an indispensable component in any direct-view-type color liquid crystal display device.
Generally, there are two types of color liquid crystal displays. One type is an active matrix driven twisted nematic (TN) liquid crystal display using thin film transistors (TFT), and another type is a multiplex driven super twisted nematic (STN) liquid crystal display. Both types of display are arranged to display pictures in such a manner that a polarizing plate, which is disposed on both surfaces of a liquid crystal device having its liquid crystal layer interposed between glass substrates, modulates the polarized state of linearly polarized light directed therethrough. More recently, various other types of displays have been proposed, such as ones using the selective reflection of cholesteric, controlling optical scattering and transmittance, optical absorption and transmittance or the like. The levels of brightness of the back light required in these note-type personal computers vary depending on their applications and specifications. However, for color note-type personal computers, it is mandatory to provide for a thin, light-weight design, with a low power consumption in addition to the requirement for a satisfactory brightness level. Still further, there is an increasing expectation for provision of a larger display screen, such as a computer display, using a liquid crystal device, and, therefore, it is necessary to provide for a display having a broader light emission property so as to provide a wider viewing angle, in addition to the provision of an improved brightness. Still more, there is a high expectancy for realization of a television having a larger display screen, wider viewing angle and a brighter liquid crystal display.
Thereby, there have been proposed and realized various methods for providing wider viewing angle liquid crystal displays, using TFTs, and operating in a multi domain vertical alignment nematic (MVA) mode, inplane switching (IPS) mode and the like. However, although these MVA and IPS modes have remarkably improved the viewing angle compared to the conventional TN, STN modes, they are associated with problems such as the occurrence of color changes and a drop in contrast ratio depending on its viewing angle and the like.
Other devices providing a wider viewing angle having no view angle dependency, which is realized on a screen which is disposed on a collimated light source and a liquid crystal display device, are disclosed in WO PCT/US94/07369, PCT/9-500981, PCT/9-505412, PCT/8-511129, PCT/9-507920, PCT/10-500528 and the like. Still other devices having screens and collimating technologies different from the above are disclosed in U.S. Pat. No. 2378252, WO PCT/US97/07374 (JPA Laid-open Nos. 6-202107 and 6-324217), respectively.
Still further, in a fluorescence color display disclosed in JPA Laid-open No. 60-50578 or in a liquid crystal display module disclosed in JPA No. 7-253576, color display devices are proposed which are comprised of an ultraviolet ray or near ultraviolet ray emitting light source; fluorescent materials for emitting red, green or blue color fluorescence disposed corresponding to liquid crystal display pixels by irradiation of ultraviolet rays; liquid crystal elements used as an optical shutter; and a color display unit for displaying a color picture by fluorescence of fluorescent materials. Still another color display unit is disclosed in JPA No. 9-80434, in which a blue color emission organic electroluminescence (EL) is used, and fluorescent material members which produce fluorescent red or green colors by irradiation of the blue light source are disposed in the form of a matrix.
Moreover, in the aforementioned display unit that uses fluorescent materials, its liquid crystal display elements function merely as an optical shutter for selectively allowing ultraviolet rays to pass, and its display is effected by fluorescence of a fluorescent material member disposed corresponding to a pixel through which ultraviolet rays have passed. Its fluorescence color is determined by a property of its fluorescent material, and a bright color rendering of red, green and blue becomes possible without absorption by a color filter, thus realizing a bright and clear color display. Still further, because a uniform spatial dispersion of light from the fluorescent materials is obtained without depending on the direction of the incident light, an improved display quality without a viewing angle dependency is realized.
The aforementioned collimating technology is associated with a problem in that its light utilization efficiency is substantially low. Further, an improved light utilization efficiency, which recently became available using a reflective polarizer based on the polarized light conversion technique disclosed, in U.S. Pat. Nos. 5486949, 5122906, SID 92 Digest p 427, JPA No. 7-36032, SID 95 Digest p 735, is insufficient and not suitable for the purpose of the invention. Still further, a construction using a prism sheet as an optical path converter which uses, for example, a brightness enhanced filter manufactured by 3M, has been disclosed for the purpose of improvement of forward directivity of light, however, its collimating property is low. Because of this low collimating property, when a wide viewing angle display is generated using fluorescent materials on a screen, unclear and bleeding color pictures are displayed due to the thickness of the glass substrates and the like.
The present invention is directed to a solution of the aforementioned problems, and is designed to provide an illumination apparatus and a liquid crystal display using the same that features a high efficiency collimating function such that an improved brightness and a wider viewing angle for a liquid crystal display can be realized. By provision of the illuminating apparatus that features an improved light utilization efficiency and a collimating function, it will become possible to realize a high brightness liquid crystal display, a wider viewing angle liquid crystal display, and a multiple liquid crystal display which displays a seamless picture on a plurality of liquid crystal displays which are aligned in a matrix array in combination without a gap.
A main object of the invention is to provide an illumination device having an improved collimating function which is realized by providing a collimating unit at a light incidence surface of a light guide, and to provide a bright liquid crystal display using the same. Another object of the invention is to provide a liquid crystal display which features a wider viewing angle by provision of a light spreading screen over liquid crystal elements. Still another object of the invention is to provide a large screen liquid crystal display system having a plurality of liquid crystal displays disposed without gap therebetween, each having a highly collimated illumination; a focus system disposed on the side of the display; a magnification system; and a screen. Still another object of the invention is to provide for a wide viewing angle and a brighter liquid crystal display having fluorescent members disposed in a matrix.
A liquid crystal display, which uses ultraviolet rays or near ultraviolet rays as a light source, and fluorescent members disposed in a matrix array has various advantages because of its monochrome light source. First of all, for a polarizer which uses a cholesteric liquid crystal layer and a retardation film, if the same is to be applied to a color liquid crystal display that uses a white light source, it is necessary for selective reflection to occur over the whole range of the visible light spectra. Otherwise, it is necessary for selective reflection to occur at least in its wavelengths corresponding to spectra of three primary colors of the light source.
However, because the actual xcex94n (birefringence) of cholesteric liquid crystal materials is approximately from 0.05 to 0.30, it is not possible for one layer of cholesteric liquid crystal material to provide for selective reflection in a broad range of wavelengths corresponding to a white light source. Therefore, in order to be able use a white light source, it is necessary to laminate a plurality of layers of cholesteric liquid crystal at a different pitch. However, when laminating the cholesteric liquid crystal layers, there occur problems of degradation in the property of the liquid crystal layer due to an increased number of interfaces and an increase in its production cost.
In addition, the retardation film used in the aforementioned polarizer has a function to convert a circularly polarized light that has passed through the cholesteric liquid crystal layer into a linearly polarized light. Therefore, in order to accommodate a white light source, it is necessary for the retardation film to be able to function as a quarter wave plate over the whole range of the visible light waves. However, generally it is impossible to construct a retardation film that can function as a quarter wave plate by provision of only one sheet thereof over the full range of the visible light waves due to its wavelength dependency (wavelength dispersion) as a result of the index of refraction of its constituting material.
In this case, it is possible to provide for a retardation plate which can function as a quarter wave plate over a wide range of wavelengths by laminating at least two different retardation plates having a different wavelength dispersion in such a way that their optical axes are arranged orthogonal to each other. However, there arises a problem in that a change depending on the angle of incidence of the light increases the in-phase differences of the retardation plates due to lamination of the retardation plates, thereby degrading its performance, now to mention the fact that the cost of manufacture increases.
On the other hand, in a color liquid crystal display which is comprised of an ultraviolet emitting light source, liquid crystal elements which are used as optical shutters, and fluorescent members which produce a fluorescent color display, because ultraviolet rays tend to be absorbed in its various transparent components, a highly efficient and bright color display as expected is not necessarily realized. Therefore, when the absorption by the various transparent components is considered, provision of a light source having a wavelength greater than 380 nm is preferable. More preferably, a light source having a wavelength greater than 430 nm, and a blue light of the three primary colors is preferably displayed using its light source color.
In particular, in case an edge backlight device is used as an illumination device, a light guide made of acrylic resin is provided for guiding light from a light source to a liquid crystal display device. However, because acrylic resin tends to absorb ultraviolet rays, it is difficult to efficiently guide ultraviolet rays to the liquid crystal display device using a light guide made of this material.
Still further, because the conventional polarizers now widely in use have a ultraviolet ray absorbent added to its protective film, most of the ultraviolet rays below 380 nm are absorbed (refer to FIG. 29). Further, with reference to FIG. 30, which shows transmittance spectra of wavelengths transmitting through liquid crystal display elements, except for the polarizer, most of the ultraviolet rays are absorbed in the transparent electrodes, alignment layers and the liquid crystal as well.
Because a large portion of the ultraviolet rays are absorbed in each part of the liquid crystal display device, as described above, it is very difficult for a high-efficiency color display device to be realized by the prior art. Still further, there occurs a problem in that the liquid crystal, alignment layers and the like are easily deteriorated by irradiation of ultraviolet rays depending on the property of their materials, thereby shortening their service life.
Still further, in the case where a liquid crystal layer of the liquid crystal display element and a fluorescent member to serve as a fluorescent emission part are disposed apart from each other, separated by a glass substrate and the like, the directivity of illumination of light (ultraviolet rays of irradiation) becomes low. Namely, when the parallelism or collimation of the light is low, the back-light illumination is allowed to stray to another fluorescent member corresponding to another pixel of the liquid crystal display different from a fluorescent member which is intended to be excited and displayed, thereby causing problems of color bleeding and deterioration of resolution. None of the aforementioned prior art considered or suggested any solution of these problems or how to improve the collimation of the illumination light.
The present invention is directed to a solution of such problems associated with the prior art, and is designed to provide an improved color display device which features an improved light utilization efficiency, improved brightness, minimized power consumption and improved quality of display without color bleeding or deterioration of resolution, realized by suppression of light absorption by color filters and/or polarizers.
In order to accomplish the objects of the invention, the following arrangements, devices, components and parts are employed.
According to one aspect of the invention for realizing an improved light utilization efficiency and improved collimation, an illumination apparatus is provided comprising: a light guide; a collimating unit provided at least on one side of the light guide for collimating incident rays to the light guide; and a light source disposed in the vicinity of the collimating unit and surrounded by a reflector. Preferably, in order for the light guide to be able to emit a collimated light uniformly from its emission surface, the light guide is comprised of inclined reflecting irregularities or stepwise reflecting plates which are provided directly or via an air gap on a back surface opposite to the emission surface thereof, wherein the inclined reflecting plates are specular-finished at least on their inclined portions. Alternatively, the light guide may be provided with inclined grooves on the emission surface thereof. More preferably, in order to be able to convert non-polarized light from the light source into a polarized light and to emit the polarized light uniformly, the light guide is provided with an irregular surface whereby light emitted from the light guide is emitted in a band, and further, a polarizing converter is provided on the light guide.
Still further, in order to be able to reduce the thickness of the illumination apparatus, an optical axis of the aforementioned collimating device is disposed so as to be tilted relative to the emission surface of the light guide. Here, the optical axis of the collimating device is defined as a peak direction of intensities of emission light f rom the collimating device.
Still more, in order for light emitted from the light source to efficiently enter into the collimating device, preferably, the light source is provided as a cylindrical light source, and the collimating device has a wide light incident opening at least along a major axis of the light source and along the light guide, and a narrow opening in the center portion of the light guide. Further, in case the light source is a spot light source, such as LED or the like, such a light source is arranged corresponding to each collimating device, and the collimating device has a narrow side on the side of the light source and a wide side on the side of the light guide. Still further, in order for light emitted from the light source to efficiently enter into the collimating device, a side wall of an expanded portion of the collimating device facing the light source is covered by a light reflecting plate.
Furthermore, a polarization converter is provided between the collimating unit and the light guide so that non-polarized light from the light source is converted to polarized light, thereby further improving its light utilization efficiency.
Still further, by providing liquid crystal display elements that display a picture by controlling a polarization state, scattering/transmittance, or absorption/transmittance of light, and arranging the illumination apparatus on the back side of the liquid crystal display elements according to the invention, a high brightness liquid crystal display device can be implemented. Further, by arranging a screen for spreading emitted light on the side of the display of the liquid crystal display elements, a liquid crystal display device having a high brightness and wide viewing angle can be implemented. Here, if a display mode is provided which ensures that the liquid crystal display elements will have a sufficient contrast ratio relative to an incident angle of light within a range of light emission angles for the light source, a wide viewing angle display free from a change in its contrast ratio depending on its viewing angle, gradation reversal, and color changes can be obtained.
Still more, by provision of a plurality of the liquid crystal display units using an illumination device having an improved collimating property according to the invention, and by disposing on the side of its display screen a focusing system formed by a microlens array etc., a magnifying unit formed by a frennel lens etc., and preferably a bead screen which has a function to absorb-external light and spread its emission light, a large display screen liquid crystal display system featuring a seamless and a broad viewing angle display can be implemented. An example of such a bead screen is disclosed, for example, in U.S. Pat. No. 2,378,252, and has a function to absorb external light efficiently and transmit emission light from the liquid crystal display elements efficiently.
Further, according to still another aspect of the invention, a liquid crystal display system is provided, which is comprised of a pair of transparent substrates disposed at a preset gap with their transparent electrode forming surfaces being placed opposite to each other; a liquid crystal layer interposed between the pair of transparent substrates; a liquid crystal display element provided with a voltage application part for applying a voltage in response to a picture signal to a pixel in a matrix formed by transparent electrodes on the pair of transparent substrates; a light source for emitting a back light to illuminate the back surface of the liquid crystal display element, the wavelength of the emission peak of which is from 380 to 500 nm; and fluorescent material members of one or more species for converting wavelengths for converting the light from the light source into red or green colors, which are disposed corresponding to each pixel of the liquid crystal display element on the side of light emission of the liquid crystal layer of the liquid crystal display element, wherein the aforementioned liquid crystal display element has a polarizer provided at least on the side of light incidence such that a polarization state of incident light to the liquid crystal layer is utilized to display a picture, and wherein, by disposing the illumination device on the back surface of the liquid crystal display element, an improved liquid crystal display system free from an absorption loss by the color filters is realized.
Further, by adopting a light for the light source having an emission peak wavelength of 430 to 480 nm, a transmittance factor of constituting components and parts, such as glass substrates, polarizers, liquid crystals and the like, can be substantially improved, thereby realizing a greatly improved high brightness liquid crystal display system.
It should be noted that in the color display device having such arrangements as described above, the light to be emitted from the light source and to be modulated in the liquid crystal display element is a monochrome (blue) light having a narrow band region. Therefore, the functions of a polarizing splitter, which is a cholesteric liquid crystal layer, the polarizing splitting capability of a linearly polarizing splitting element, or a phase retardation plate of the polarization converter become higher than in a case of white light which has a broader band region.
Therefore, the non-polarized light from the light source is converted more efficiently than the prior art into a preferred linearly polarized light, namely, into a linearly polarized light, the oscillation direction of electric vectors of which is identical with the linearly polarized light transmittance axis of a polarizer which is disposed on the back side of the liquid crystal display element, and then is irradiated on the liquid crystal display element. Thereby, most of the light incident on the liquid crystal display element contributes to the purpose of the display without being absorbed in the polarizer, thereby more efficiently utilizing the light from the light source without wasting light due to absorption by the polarizer.
Still further, the liquid crystal display element of the invention functions as an optical shutter for allowing only a blue color of the light source to be selectively transmitted therethrough, and the display of green and red colors are enabled by fluorescence of fluorescent material members which are patterned at respective positions corresponding to respective pixel colors. Further, display of the color blue is enabled by light transmitted through a blue color filter which is patterned corresponding to the positions of blue color pixels. However, because the light source is a blue color emission source, there will occur no loss of transmittance through the blue color filter. Thereby, a bright color display device is provided featuring an improved light utilization efficiency and no loss of light transmittance through the color filters compared to the prior art.
Still more, because back-light illumination light emitted from the light source is collimated in omnidirections effected by the inclined reflecting surface formed in the bottom surface of the light guide and the optical path conversion device, even if the liquid crystal layer of the liquid crystal display element and the fluorescent members of the wavelength converter are separated by the glass substrate from each other, the straying of light of the illumination light from its destined fluorescent member corresponding to a pixel to be energized is minimized, thereby suppressing the occurrences of color bleeding, and deterioration of the resolution, so as to provide for an improved and enhanced quality of color display.
Still further, because the excitation source light (light source) for use in the fluorescence display produces visible light, it is not absorbed by various transparent materials used in the liquid crystal display element as the ultraviolet rays were absorbed, the light from the light source is most efficiently utilized, and no deterioration of the polarizers, liquid crystal material or the like by ultraviolet rays occurs, thereby providing for a long service life fluorescent color display device.
Furthermore, in the color display device according to the invention, a band pass filter is provided at a portion of the wavelength converter where no blue color filter is pattern-formed, namely, at a portion where the fluorescent member is pattern-formed, and at a position in the upper direction of the fluorescent member near to the viewer, this band pass filter allows emission spectra of the red and the green color emission fluorescent members to pass, and cuts off other spectra of light.
In this case, because excitation light contained in external light is absorbed in the band pass filter, no enhanced brightness black color display occurs due to excitation of the fluorescent members. Further, red and green colors generated by fluorescence of the fluorescent members are allowed to pass through without being absorbed in the band pass filter, and the blue color for which no band pass filter is provided in its blue color filter section can contribute wholly to the purpose of the display without absorption, thereby providing for a substantially improved contrast ratio even under day-light or illuminated circumstances.
Still further, by provision of a reflecting layer on the back surface of the wavelength converter (on the side of the liquid crystal display element) which allows the emission spectra from the light source to pass, but reflects other incoming visible light, a loss of light due to return of scattered light produced by fluorescence from the fluorescent members to the liquid crystal display element can be minimized, or deterioration of the display quality, such as color bleeding and the like, due to stray light can be eliminated, thereby realizing an improved color display device featuring a brighter display quality.